JP3332201B2 - Flow control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate control method applied to liquids such as liquids and fluids, and more particularly to a flow rate control method suitable for flow rate control of water for cooling wire.

[0002]

2. Description of the Related Art Conventionally, for example, in a water amount control method for cooling a wire rod applied to the cooling of a rod material such as a steel bar, the flow control P
A PI control method is adopted in which the (proportional) and I (integral) gains are made variable, the variable gains are changed according to the flow rate set value, and the gains are multiplied by a control deviation to perform proportional control. That is, the relationship between the flow rate and the P and I gains is determined in advance, and based on the relationship, the flow rate control is performed to increase the P and I gains as the flow rate setting value increases.

[0003]

However, in the method of changing the P and I variable gains of the flow control in accordance with the flow rate set value, when the flow rate setting is changed, the P and I variable gains are changed.
If the setting is changed to increase the I gain, the control response can be made faster. Conversely, if the setting is changed to decrease the P and I gains, the control response corresponding to the flow rate becomes lower. Since the gain is set, there is a problem that the gain becomes smaller than necessary and the control response becomes slower accordingly.

The present invention has been made in order to solve the above-mentioned conventional problems. When the P and I gains of the flow rate control are changed according to the flow rate using a relation created in advance,
When the P and I gains corresponding to the flow rate setting values to be changed are small, the P and I gains can be prevented from lowering unnecessarily and the flow control can be prevented from causing a delay in the control response at the time of changing the flow rate setting. It is an object to provide a method.

[0005]

SUMMARY OF THE INVENTION According to the present invention, there is provided a flow rate control method for controlling the flow rate of a fluid by changing the P and I gains of the control based on a relationship between the flow rate of the fluid and the P and I gains prepared in advance. In the control method, when the flow rate is changed, if the P and I gains corresponding to the flow rate set this time are higher than the previous time, the P and I gains are changed to the P and I gains corresponding to the flow rate set value.
When the P and I gains corresponding to the flow rate set this time are lower than the previous time, the above problem is solved by changing to the P and I gains corresponding to the actual flow rate values.

That is, in the present invention, when the flow rate is controlled by changing the P and I gains according to the flow rate by using a relationship created in advance, the flow rate set value is changed in a direction to decrease the gain. In this case, the gain is changed not by the set value but by the actual flow rate value, so that it is possible to prevent a delay in the control response when the flow rate setting is changed.

According to the present invention, as a result of various studies, it is conceivable that the setting of the P and I gains may be changed only based on the actual flow rate value. Since the control response is slower than the change of the P and I gains by the set value, the change by the flow rate set value can be selected in the direction of decreasing the gain, and the change by the flow rate set value can be selected in the direction of increasing the gain. It is made after finding that the above is effective.

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a flow control device applied to an embodiment according to the present invention.

The flow rate control device applied to the present embodiment is applied to flow rate control of cooling water used for cooling a wire rod, and selects either a flow rate actual value or a flow rate set value according to a change direction of a flow rate set value. And a function of changing the P and I gains based on the values.

The flow control device includes an input processing unit 10 for inputting a flow actual value PV actually measured by a flow measured value (not shown) and a flow set value SV and performing a predetermined process, and a schedule to be set this time. Flow set value SVn and the previously set flow set value S
Vn-1; a difference calculating unit 12 for calculating a difference from the set value SVn; an SV increasing / decreasing direction comparator 14 for determining whether or not the current set value SVn is larger than the previous set value SVn-1; 14, the set value SVn is input from the input processing unit 10 when the value is increased, and the set value SV and the actual value PV are input when the value is decreased. And a changeover switch 16 for selecting and switching the PV.

Further, the control device performs the following operations based on the set value SV or the actual value PV of the flow rate selected by the switch 16.
P and I variable gain linearize 18 for calculating corresponding P and I gains from a gain curve (relation between flow rate and P and I gains) prepared in advance, and a control deviation input from the input processing unit 10 A corresponding to DV (PV-SV),
A multiplier 20 for multiplying by the P and I gains b obtained by the linearization 18; a PID calculator 22 for calculating a control signal based on the result of the multiplication by the multiplier 20; Control valve control signal MV (Moved Value) for controlling the flow rate based on the obtained control signal
And an output unit 24 for outputting

In the present embodiment, the difference calculator 1
2. Through the respective processes by the SV increase / decrease direction comparator 14 and the changeover switch 16, the direction of increase / decrease of the flow rate when the set value SV is changed is determined. Selects the actual value PV and outputs the value of SV or PV to the linearize 18. In this linearize 18, P and I gains are calculated from the previously set gain curve based on the input SV or PV value, and output to the multiplier 20. In this multiplier 20,
The control deviation a is multiplied by the gain b input from the linearize 18, the result is output to the PID calculator 22, and the flow rate is controlled.

According to this embodiment, when the flow rate setting is changed,
When changing in the direction to increase the gain, set the flow rate set value SV
Is selected, the P and I gains are changed to values determined based on the set values, and when the gain is changed in a direction of decreasing the gain,
The actual flow value PV is selected, and the P and I gains are changed to values determined based on the actual value.

Therefore, when the flow rate set value is changed, the control can be started immediately with the large P and I gains determined from the flow rate set value in the direction of increasing the gain. By changing to a value determined from the actual value PV and not immediately setting a small gain corresponding to the set value, it is possible to perform control while gradually reducing the gain. As a result, it is possible to obtain a quick control response to a setting change in any of the upper and lower directions of the flow rate set value.

FIG. 2 shows P, I based on only the flow rate set value.
FIG. 3 is a diagram showing a control result (control responsiveness) when a conventional control method for setting a gain is applied in a direction of decreasing the gain. FIG. 3 shows a flow control method according to the present invention. It is a diagram showing a result when applied under the same conditions.

When comparing FIG. 2 with FIG. 3, the control response was slow (the response was low) because the P and I gains were conventionally changed by the set value SV even in the direction of decreasing the gain. On the other hand, according to the present invention, in the direction of decreasing the gain, the actual value PV is selected instead of the set value SV, and the gain is changed based on the selected value. It can be seen that the control response is improved (response is improved) to about twice the speed as compared with the method described above, and a good result is obtained.

Although the present invention has been specifically described above, the present invention is not limited to the above-described embodiment, and can be variously modified without departing from the gist thereof.

For example, in the above embodiment, the case of controlling the flow rate of the cooling water for the wire rod has been described. However, the present invention is not limited to this, and the present invention may be applied to the control of the flow rate of another liquid or gas. .

[0020]

As described above, according to the present invention,
When the P and I gains of the flow rate control are changed in accordance with the flow rate using a relation created in advance, even when the P and I gains corresponding to the flow rate set values to be changed are small, the P and I gains are changed. Can be prevented from unnecessarily lowering, and a delay in control response when changing the flow rate setting can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a flow control device applied to an embodiment of the present invention.

FIG. 2 is a diagram showing a control result by a conventional control method.

FIG. 3 is a diagram showing a control result according to the present invention;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Input processing part 12 ... Difference calculation part 14 ... SV increase / decrease direction comparator 16 ... Changeover switch 18 ... Linearize for P and I variable gain 20 ... Multiplier 22 ... PID calculator 24 ... Output

Claims (1)

(57) [Claims] A P and I gain for control is changed based on a relationship between a fluid flow rate and a P and I gain created in advance.
In the flow rate control method for controlling the flow rate of the fluid, when changing the flow rate, if the P and I gains corresponding to the flow rate set this time are higher than the previous time, the P and I gains corresponding to the flow rate set value will be changed. A flow control method, wherein the P and I gains corresponding to the flow rates set this time are changed to P and I gains corresponding to the actual flow rate values when the P and I gains corresponding to the flow rates set this time are lower than the previous time.